Apparatus and method for adaptive channel transmission using channel state

ABSTRACT

The present invention relates to an apparatus and method for adaptive channel transmission using a channel state, and according to one embodiment of the present invention, a method for channel transmission of a remote node includes intermittently receiving a forward channel transmitted from a host node, estimating a reverse channel state based on the received forward channel, determining whether the estimated reverse channel state satisfies a preset channel condition, and adaptively transmitting a reverse channel based on the determined result.

TECHNICAL FIELD

The present invention relates to an apparatus and method for channeltransmission, and more particularly, to an apparatus and method forchannel transmission, in communication between a host node and a remotenode, that adaptively transmits a reverse channel from the remote nodeto the host node in consideration of a state of a communication channel,and a recording medium recording the method.

BACKGROUND ART

The development of electronic technologies has promoted the developmentof telecommunication using an electromagnetic wave as a medium, andtelecommunication has expanded and is being used as various types ofwireless communications of the day. Basically, wireless communicationmodulates information to be transmitted to a radio wave and transmitsthe radio wave through a power amplifier (PA), so that the receivedradio wave is demodulated at the side of a receiver to obtain theinformation.

To improve the efficiency of wireless communication, researchersintroduced a concept of time division that configures different messagechannels for each time slot in a non-overlapping manner of the messagechannels by temporally separating the respective messages, to allowparallel transmission over a single transmission medium. Using this timedivision, a pulse of one communication path can be inserted using a restperiod between pulses on another communication path, thereby allowingtemporally different multiple communications. Particularly, in the timedivision transmission scheme, a scheme that enables bidirectionalcommunications using one frequency by dividing one frame into atransmission part and a reception part is referred to as time divisionduplex (TDD). Generally, wireless communication uses differentfrequencies for transmission and reception, while a TDD scheme ischaracterized in that a single frequency is temporally divided forseparate use of transmission and reception, thereby allowingbidirectional communications.

Meanwhile, a TDD-based wireless communication system and a remote node(or a wireless communication terminal) for use therein receive a signalfrom a host node and transmit its own signal to the host node. With thefunctional diversity and structural complexity of the remote node, inturn, a difficulty in power management occurred to the remote node.Particularly, with the advanced function of the remote node, variousstudies have been proposed to save the power consumed by the remote nodemaking a mutual communication with the host node. The non-patentliterature as stated below indicates a situation in which excessivepower is consumed in reverse channel transmission from a remote node toa host node.

(Non-patent Literature 1) Hichan Moon, Suhan Choi, “Channel adaptiverandom access for TDD-based wireless systems”, IEEE Trans. VehicularTech., pp. 2730-2741, July 2011.

DISCLOSURE Technical Problem

The present invention is designed to solve a problem that efficiency ofchannel transmission reduces due to a remote node in a wirelesscommunication system transmitting a reverse channel upon receiving aforward channel from a host node without considering a channel state, toprevent unnecessary power consumption by leaving power consumed inmeasuring the forward channel received from the host node out ofconsideration, and to overcome the limitation of transmissionperformance caused by the reverse channel transmission of the remotenode without considering a change in the channel state.

Technical Solution

To solve the technical problem, a method for channel transmission of aremote node according to one embodiment of the present disclosureincludes intermittently receiving a forward channel transmitted from ahost node, estimating a state of a reverse channel from the remote nodeto the host node based on the received forward channel, determiningwhether the estimated state of the reverse channel satisfies a presetchannel condition, and adaptively transmitting the reverse channel basedon the determined result.

In the method for channel transmission of the remote node according toone embodiment, the receiving of the forward channel is performed bymeasuring the forward channel by the remote node enabling an operationof a receiver for only a first period, and not measuring the forwardchannel by stopping the operation of the receiver for a second periodapart from the first period, and the first period during which thereceiver operates and the second period during which the receiver doesnot operate are arranged repetitively in a flow of time. Also, in themethod for channel transmission of the remote node according to oneembodiment, it is possible to set different time interval values betweenthe plurality of first periods arranged repetitively.

In the method for channel transmission of the remote node according toone embodiment, the receiving of the forward channel includes setting anext measurement time, comparing the set next measurement time to apresent time, and when the next measurement time corresponds to thepresent time as a result of the comparison, measuring the forwardchannel by the remote node enabling an operation of a receiver. On thecontrary, when the next measurement time does not correspond to thepresent time, the remote node repeats the comparison step after stoppingan operation of a receiver and standing by for a predetermined time.

To solve the technical problem, a method for channel transmission of aremote node according to another embodiment of the present inventionincludes receiving a forward channel transmitted from a host node,estimating a state of a reverse channel from the remote node to the hostnode based on the received forward channel, determining whether theestimated state of the reverse channel satisfies a preset channelcondition, and adaptively transmitting the reverse channel based on thedetermined result, and the channel condition is variably reset overtime.

Also, in the method for channel transmission of the remote nodeaccording to another embodiment, the determining of whether theestimated state of the reverse channel satisfies the preset channelcondition is performed by comparing a state estimate of the reversechannel calculated based on a channel gain of the received forwardchannel to a threshold representing the channel condition.

Further, hereinafter, there is provided a computer-readable recordingmedium having a program for causing a computer to execute the abovemethods for channel transmission of the remote node stored therein.

To solve the technical problem, a remote node according to still anotherembodiment of the present invention includes a receiving unit tointermittently receive a forward channel transmitted from a host node, achannel estimating unit to estimate a state of a reverse channel fromthe remote node to the host node based on the received forward channel,a control unit to determine whether the estimated state of the reversechannel satisfies a preset channel condition and determine whether totransmit the reverse channel based on the determined result, and atransmitting unit to adaptively transmit the reverse channel based onthe determination of the control unit.

In the remote node according to still another embodiment, the receivingunit measures the forward channel by operating for only a first periodand does not measure the forward channel turning off the receiver for asecond period apart from the first period, and the first period duringwhich the receiver operates and the second period during which thereceiver does not operate are arranged repetitively in a flow of time.Also, in the remote node according to still another embodiment, it ispossible to set different time interval values between the plurality offirst periods arranged repetitively.

In the remote node according to still another embodiment, the channelcondition may be variably reset over time.

In the remote node according to still another embodiment, the controlunit determines whether to transmit the reverse channel by comparing astate estimate of the reverse channel calculated based on a channel gainof the received forward channel to a threshold representing the channelcondition.

Advantageous Effects

The embodiments of the present invention may improve the efficiency ofchannel transmission by enabling a remote node to transmit a reversechannel with a delay in consideration of a channel state rather thanmaking a response immediately upon receiving a forward channel from ahost node, may reduce unnecessary power consumption involving channelreception by intermittently measuring the forward channel received fromthe host node, and may optimize the performance of reverse channeltransmission by variably setting a channel condition in consideration ofa change in the channel state.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a signal transmission structure of aforward channel and a reverse channel under a wireless communicationenvironment in which the embodiments of the present invention areimplemented.

FIG. 2 is a diagram illustrating a structure of an access probe (AP)transmitted through the reverse channel in the wireless communicationenvironment of FIG. 1.

FIGS. 3a and 3b are diagrams each illustrating a pilot channeltransmitted under a wireless communication environment in which theembodiments of the present invention are implemented and a referencesignal transmitted in a forward direction.

FIGS. 4a and 4b are diagrams illustrating methods of intermittentlyreceiving a forward channel employed by the embodiments of the presentinvention.

FIG. 5 is a flowchart illustrating a method for channel transmission ofa remote node according to an exemplary embodiment of the presentinvention.

FIG. 6 is a flowchart illustrating more specifically a method ofcontrolling intermittent reception of a forward channel and transmissionof a reverse channel based on a channel condition in the method of FIG.5 according to an exemplary embodiment of the present invention.

FIG. 7 is a diagram illustrating an example of a message for a host nodeto transmit information about a channel state measurement cycle of aforward channel to a remote node.

FIGS. 8a and 8b are diagrams illustrating methods of changing atransmission condition in channel transmission of a remote nodeaccording to another exemplary embodiment of the present invention.

FIG. 9 is a block diagram illustrating a remote node communicating witha host node according to still another exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF MAIN ELEMENTS

900: Remote node

10: Antenna

20: Receiving unit

30: transmitting unit

40: Channel estimating unit

50: Control unit

60: Doppler frequency measuring unit

[Best Mode]

According to one embodiment of the present invention, a method forchannel transmission of a remote node includes intermittently receivinga forward channel transmitted from a host node, estimating a state of areverse channel from the remote node to the host node based on thereceived forward channel, determining whether the estimated state of thereverse channel satisfies a preset channel condition, and adaptivelytransmitting the reverse channel based on the determined result.

According to another embodiment of the present invention, a method forchannel transmission of a remote node includes receiving a forwardchannel transmitted from a host node, estimating a state of a reversechannel from the remote node to the host node based on the receivedforward channel, determining whether the estimated state of the reversechannel satisfies a preset channel condition, and adaptivelytransmitting the reverse channel based on the determined result, and thechannel condition is variably reset over time.

[Mode for Invention]

Prior to the description of the embodiments of the present invention, awireless communication environment in which the embodiments of thepresent invention are implemented, and an implementation problemoccurring in the environment in which the embodiments of the presentinvention are implemented and a solution to the problem will be nowpresented briefly.

The embodiments of the present invention are widely applicable to awireless communication system using time division duplex (TDD).Hereinafter, the term ‘host node’ will be used to represent a nodetransmitting a signal through a forward link, and the term ‘remote node’will be used to represent a node transmitting a signal through a reverselink. Take note of a random access channel used in a mobilecommunication system that is a type of wireless communication system,for example, Wideband Code Division Multiple Access (W-CDMA) or LongTerm Evolution (LTE) by the Third Generation Partnership Project (3GPP)or CDMA2000 by 3GPP2. First, assuming a W-CDMA system, a description ofrandom access channel transmission is provided with reference to FIG. 1.

FIG. 1 is a diagram illustrating a signal transmission structure of aforward channel and a reverse channel under a wireless communicationenvironment in which the embodiments of the present invention areimplemented, and a remote node transmits a signal through a randomaccess channel (representing a reverse channel) as shown in FIG. 1.

In FIG. 1, assume that a forward channel is an accesspreamble-acquisition indication channel (AP-AICH), and a reverse channelis a random access channel (RACH). As shown in the drawing, the remotenode transmits a preamble through a random access channel of a reverselink for initial synchronization of communication. In this instance, theremote node transmits an access probe (AP) AP0 110 including a preamblethrough the random access channel. For example, the remote nodetransmits an access probe consisting of a preamble as shown in (A) ofFIG. 2 through the random access channel.

In case the remote node does not receive a response signal to the accessprobe AP0 110 from the host node for a time period of tp-p, the remotenode re-transmits, through the random access channel, an AP1 120 with anincreased transmission power by ΔP in comparison to the access probe AP0110. In this instance, the access probe AP1 120 includes a preambleconsisting of a same signature as the access probe AP0 110 transmittedpreviously.

Then, when the host node receives the access probe AP1 120 through therandom access channel, the host node stands by for a time period oftp-ai and transmits a same signature as the received access probe AP1120 to the remote node through an AICH 130. Then, the remote nodeidentifies the signature and an acquisition indicator (AI) (not shown)by demodulating a signal received through the AICH 130. In case anacknowledgement (ACK) signal of the host node is identified through theacquisition indicator, the remote node stands for the time period oftp-ai again and transmits a message including reverse data to the hostnode through the reverse random access channel. For example, the remotenode transmits an access probe including a message configured as shownin (B) of FIG. 2 through the random access channel. In this instance,the remote node transmits the corresponding access probe with atransmission power corresponding to the access probe AP1 120.

FIG. 2 is a diagram illustrating a structure of the access probe (AP)transmitted through the reverse channel in the wireless communicationenvironment of FIG. 1, and assuming CDMA2000 by 3GPP2. In case an accessprobe including a message shown in (B) of FIG. 2 is transmitted from theremote node and is successively received by the host node, the 3GPP2CDMA2000 random access channel provides a reception notification to theremote node through a forward common channel. That is, this signal istransmitted as a message via the forward common channel without AICHtransmission.

As described in the foregoing, a majority of random access channels isan essential element of a wireless communication system, and a randomaccess channel is implemented through various methods. Despite variousimplementation methods, a conventional random access channel merely hastransmitted an access probe immediately upon occurrence of an event thataims to transmit a random access channel on an upper layer, withoutconsidering a channel state of a reverse link. However, this promptrandom access channel transmission has a problem that excessivetransmission power is required.

To solve this problem, a sort of transmission delay method may beproposed in which a time division duplex-based wireless communicationsystem obtains information of a reverse channel state by measuring astate of a forward channel, and transmits a random access channel onlywhen the obtained information satisfies a particular transmissioncondition. By determining whether to transmit the random access channelbased on the channel state and delaying the transmission of the randomaccess channel access probe when the transmission condition is notsatisfied, a transmission output may be significantly reduced. Also, acoverage radius of the communication system may be greatly expandedunder the same maximum or average transmission output condition.

In sum, the above-mentioned channel adaptive random access channeltransmission scheme enabled a remote node to determine a random accesschannel transmission condition in advance, to measure a forward channel,and when the forward channel satisfies a transmission condition, totransmit a random access channel, and otherwise, to delay the randomaccess channel transmission. That is, a transmission power used intransmission may be significantly reduced by transmitting a randomaccess channel only when a channel state is good.

However, power consumed by the remote node is not only a transmissionpower of the random access channel, but also a great amount of powerrequired to operate a receiver to measure the forward channel. In thesimple channel adaptive random access channel discussed in theforegoing, power consumed in measuring the forward channel was notconsidered.

Meanwhile, in the conventional channel adaptive random access channel,once a transmission condition is determined, optimizing the transmissioncondition by changing the transmission condition was not contemplated.Accordingly, it was impossible to flexibly respond to a change inchannel state. In relation to this, in many wireless communicationsystems, there may exist a required condition that a message of a randomaccess channel should be transmitted within a predetermined time. Underthis situation, in case transmission of a random access probe is delayeddue to a bad channel state, performance of a channel adaptive randomaccess channel may be further improved by changing a transmissioncondition based on an elapsed time (or a time left for subsequent randomaccess channel transmission).

FIGS. 3a and 3b are diagrams each illustrating a pilot channeltransmitted under a wireless communication environment in which theembodiments of the present invention are implemented and a referencesignal transmitted in a forward direction. Generally, in many wirelesscommunication systems, a host node transmits a pilot or a referencesignal continuously or periodically via a forward link. Under thiswireless communication environment, according to the embodiments of thepresent invention, a remote node measures a forward channel transmittedby the host node and estimates a reverse channel state based on themeasured result.

FIG. 3a illustrates a pilot channel transmitted in CDMA2000 or W-CDMA.Referring to FIG. 3a , in case a pilot channel exists as one codechannel, the pilot channel is always transmitted continuously.Accordingly, a remote node may measure a state of a forward channel bymeasuring the pilot channel. As described previously, when transmittinga random access channel, a conventional CDMA2000 or W-CDMA systemtransmitted a random access channel immediately upon occurrence of anevent of triggering the random access channel on an upper layer. In thisinstance, to determine a transmission power for transmitting the randomaccess channel, a state of a forward channel was measured. That is, thepilot channel being transmitted via the forward channel was continuouslymeasured and used to determine the transmission power of the randomaccess channel. Accordingly, it can be seen that power consumption bythe remote node receiving the forward channel may take place in theprocess of transmitting the reverse channel (random access channel).

FIG. 3b illustrates an implementation example of a reference signaltransmitted in a forward direction in 3GPP LTE. In FIG. 3b , onesubframe is transmitted with a length of 1 millisecond (ms), and eachsubframe is made up of 14 orthogonal frequency-division multiplexing(OFDM) symbols. The reference signal is transmitted for only a period ofa certain symbol among the symbols. In the LTE system, the referencesignal is transmitted in every 1st, 5th, 8th, and 12th OFDM symbols, andusing this, a state of a forward channel may be measured. However, incase transmission of a random access channel is needed, a remote nodecontinuously monitors a forward channel. For the convenience ofdescription, FIG. 3 b illustrates a reference signal under theassumption that the reference signal is transmitted in only two symbolsof a subframe. That is, although FIG. 3b shows one subframe, thissubframe structure has a structure of repeating unlimitedly on a timeaxis. Thus, a remote node can measure a channel state of a forwardchannel in all the subframes.

Now, assume that an event of an upper layer occurs under the abovewireless communication environment. In the conventional random accesschannel transmission scheme, a random access channel was transmittedimmediately when an event of an upper layer occurred. On the contrary,in a channel adaptive random access channel employed in the embodimentsof the present invention, an access probe of a random access channel istransmitted only when a preset channel condition is satisfied, andotherwise, access probe transmission is delayed.

In case a random access channel is to be transmitted via only a channelin a very good state to minimize a transmission power, it may take avery long time before transmitting an access probe. In this case, interms of overall power consumption of a terminal, power required tomeasure a forward channel may be relatively greater than a transmissionpower. Particularly, in the case of channel adaptive random accesschannel transmission, a transmission delay of an access probe may rangefrom several ms up to several seconds due to its operationalcharacteristics. Even in this case, if a remote node continuouslymeasures a state of a forward channel by operating a receiver, there isa concern that power consumption of the remote node receiver willfunction as a main factor of overall power consumption.

For example, assume that power consumption by a remote node transmittinga random access channel is 500 milliwatt (mW), and the remote nodetransmits the random access channel for total 5 ms, including a message.In this case, energy consumed by a transmitter is 2.5×10⁻³ J in total.On the contrary, in case power is 50 mW when only a receiver operatesand a transmission delay in channel adaptive random access channeltransmission is 1 second, power consumed by a receiver is 50×10⁻³ J intotal, so that a situation occurs in which the power consumed by thereceiver is greater about 20 times than the transmission power.

To solve the above problems, hereinafter, various embodiments of thepresent invention are described in detail with reference to theaccompanying drawings. In the description of the invention, a detaileddescription of related known functions or structures is omitted if it isdeemed to obscure the subject matter of the present invention. Theembodiments of the present invention may be used to reduce atransmission power required for a reverse random access channel or toexpand a coverage radius of a terminal having a limited maximumtransmission output or average transmission output in the field ofmobile communication. Also, the embodiments of the present invention maybe used in all types of communication systems and terminals needed tominimize the power required for communications, for example, a sensornetwork, a wireless local area network (LAN), machine-to-machinecommunication, and communication between medical equipments.

FIGS. 4a and 4b are diagrams illustrating methods of intermittentlyreceiving a forward channel employed by the embodiments of the presentinvention, and demonstrates an operation of a receiver equipped in aremote node.

Basically, the embodiments of the present invention estimate a state ofa reverse channel through receiving and measuring a forward channel, andtransmit a reverse channel in consideration of a set channel state.However, in this case, there exists a concern about a waste of powercaused by power consumed while receiving a forward channel based on achannel state as indicated previously. To solve this problem, thepresent invention proposes a method that reduces overall powerconsumption of a remote node by repeating a process of enablingoperation of a receiver for a predetermined period and a process ofenabling non-operation of the receiver for a predetermined period,rather than measuring a state of a forward channel by continuouslyoperating a receiver of a terminal.

First, in case there is a need to transmit a random access channel, aremote node measures a forward channel and determines whether totransmit the forward channel. The remote node performs a forward channelmeasurement for a certain time period, and determines whether totransmit an access probe based on the measured result. Also, the remotenode does not operate a receiver of the remote node for a time duringwhich the forward channel measurement is not performed, so that powerconsumption of the remote node may be reduced. Particularly, powerconsumption may be minimized by powering off a majority of blocks for atime period during which the remote node does not measure the forwardchannel, except an essential part for operation of the remote node, forexample, a clock to measure a time of the remote node. That is, theremote node may reduce power consumption by operating similar to a sleepstate of a mobile communication terminal.

In FIG. 4a , a remote node measuring a state of a forward channel in auniform cycle is shown for each period. In FIG. 4a , a measurementinterval was set to maintain a uniform time interval (T1=T2) all overthe measurement intervals. A point in time at which the remote nodeoperates the receiver to measure the state of the forward channel may bedetermined by various methods. First, assume that the remote nodemeasures a Doppler frequency of the channel by embedding a Dopplerfrequency measurer in the receiver or is already aware of an estimatedvalue of a Doppler frequency of the channel between the remote node andthe host node. In this case, the remote node may determine a measurementcycle of the state of the forward channel as a function of the Dopplerfrequency of the channel. The embodiments of the present invention mayadjust an interval of the forward channel measurement period shown inFIG. 4a according to the determined measurement cycle. This timeinterval may be determined in inverse proportion to the Dopplerfrequency. That is, when the Doppler frequency of the channel is high,the time interval between measurement periods of the state of theforward channel is set to be short, and when the Doppler frequency ofthe channel is low, the time interval between measurement periods of thestate of the forward channel is set to be long.

Also, the time interval between measurement periods may be adjustedbased on another parameter. For example, the time interval betweenmeasurement periods of the forward channel may be adjusted in proportionto a time allowed to transmit a random access channel. That is, when theallowed transmission time is long, there is no need to perform a forwardchannel measurement in a high-frequency. Therefore, when the allowedtransmission time is long, the time interval between measurement periodsis set to be long, and when the allowed transmission time is short, thetime interval between measurement periods is set to be short, and in theend, power consumption in a remote station may be optimized.

As a method of setting the time interval between measurement periods, aninitially set time interval may be fixedly used until an access probe istransmitted. However, more efficient random access channel transmissionmay be achieved by varying the time interval over time. That is, thetime interval between measurement periods may be variably set based onan elapsed time from the time of occurrence of an event that aims toinitially transmit a random access channel or a left time allowed tofinally transmit a random access channel. When the elapsed time from thetime of occurrence of the initial transmission event is long or theallowed left time is shortened, the time interval between measurementperiods may be set to be short, thereby designing to increase a numberof measurements.

FIG. 4b illustrates an example of variably setting the time intervalbetween measurement periods over time. Referring to FIG. 4b , the remotenode performs a forward channel measurement from a point in time t0 atwhich initial random access channel transmission is determined. However,because a channel state at this time does not satisfy a transmissioncondition, a terminal stops the operation of the receiver until a pointin time t1, and performs a forward channel measurement again from thepoint in time t1. In this instance, a time interval between t0 and t1 isT3. The remote node performs a forward channel measurement at the pointin time t1. In case a channel state at this time still does not satisfythe transmission condition, the operation of the receiver is paused fora predetermined period and the forward channel measurement is performedagain at a point in time t2. In this instance, a time interval betweent1 and t2 is T4. As illustrated in FIG. 4b , it can be seen that T4 isshorter than T3. Accordingly, overall power consumption of the remotenode may be optimized by varying the time interval between measurementperiods over time. Particularly, overall performance may be improved bysetting the time interval between measurement periods to be short overtime as illustrated in the embodiment of FIG. 4 b.

In case a pilot is not continuously transmitted on a time axis as shownin FIG. 3b , it is construed that certain subframes or pilots on thetime axis are used to measure the channel state of the forward channeland the other subframes or pilots are not used to measure the channelstate of the forward channel. Therefore, even when a pilot isintermittently transmitted as shown in FIG. 3b , the remote node usesonly some pilots in the forward channel measurement while disregardingthe other pilots, rather than using all the pilots in the forwardchannel measurement.

Meanwhile, the time interval may be changed in a way of increasing thecorresponding time interval as well as reducing the time interval asshown through the embodiment of FIG. 4b . For example, the time intervalbetween forward channel measurement periods may be adjusted to a widerinterval under various situations, such as a case in which the receiverssenses a change in the Doppler frequency of the channel after startingthe random access channel transmission, a case in which a QoS of amessage desired to be transmitted changes, or a case in which a changein condition of the time allowed to transmit a random access channeloccurs.

As described in the foregoing, in case the forward channel measurementof the remote node operates intermittently, it is possible to optimizepower consumption of the system by varying the time interval.

FIG. 5 is a flowchart illustrating a method for channel transmission ofa remote node according to an exemplary embodiment of the presentinvention, and the method includes the following steps.

In step 510, the remote node intermittently receives a forward channeltransmitted from a host node. For intermittent reception, the remotenode measures the forward channel by enabling operation of a receiverfor only a first period, and does not measure the forward channel bystopping the operation of the receiver for a second period apart fromthe first period. In this instance, the first period during which thereceiver operates and the second period during which the receiver doesnot operate may be arranged repetitively in the flow of time.

Also, the time interval between the plurality of first periods arrangedrepetitively (that is, a receiving cycle of the forward channel) may bevariably set based on at least one of a Doppler frequency of thereceived forward channel, a time allowed to transmit a reverse channel,an elapsed time from the time of occurrence of an event that aims totransmit a reverse channel, or a required level of a set QoS, and arequest from a host. More specifically, the receiving cycle of theforward channel may be in inverse proportion to the Doppler frequency ofthe received forward channel, may be in proportion to the time allowedto transmit the reverse channel, may be in inverse proportion to thetime of occurrence of the event that aims to transmit the reversechannel, and may be in inverse proportion to the required level of theset QoS.

In step 520, the remote node estimates a state of a reverse channel fromthe remote node to the host node based on the forward channel receivedthrough step 510.

In step 530, the remote node determines whether the state of the forwardchannel estimated through step 520 satisfies a preset channel condition,and in step 540, transmits a reverse channel adaptively based on thedetermined result. In this instance, a transmission power fortransmitting the reverse channel may be determined by estimating thestate of the reverse channel through measuring a pilot channel includedin the forward channel transmitted through step 510.

FIG. 6 is a flowchart illustrating more specifically a method ofcontrolling the intermittent reception of the forward channel and thetransmission of the reverse channel based on the channel condition inthe method of FIG. 5 according to an exemplary embodiment of the presentinvention.

In step 610, the remote node sets a next measurement time at which theremote node intends to receive the forward channel and a thresholdrepresenting the channel condition for access probe transmission. In thecase of channel adaptive random access channel transmission, measuringthe forward channel immediately without a time delay will be efficientfor an initial measurement time.

Through step 620, the remote node examines whether a receiving time ofthe forward channel is reached by comparing the next measurement time toa present time. If the measurement time is not yet reached, the remotenode performs step 630 to stop the operation of the receiver and standby for a predetermined time until the next measurement time is reached.Through this standby process, power consumption may be reduced.

On the contrary, as a result of the examination through step 620, whenthe next measurement time is reached, the remote node performs step 640to measure the forward channel after operating the receiver. Themeasured forward channel may be used to estimate a state of a reversechannel.

In step 650, the remote node compares a channel state estimatecalculated from the measured result through step 640 to the presetthreshold (representing the channel condition). If the channel statesatisfies the preset channel condition (that is, the channel stateestimate is greater than the threshold), the remote node performs step660 to transmit a reverse channel including an access probe.

On the contrary, if the channel state does not satisfy the presetchannel condition, the remote node reverts to step 610 and repeats aseries of the steps. In this instance, the remote node may reset thenext measurement time and the threshold.

The embodiments of the present invention proposed through FIGS. 5 and 6above employed a method that intermittently performs a channel statemeasurement of the forward channel for only a certain time and does notoperate the remote node receiver for the rest of the period to optimizepower consumption of the remote node applying the channel adaptiverandom access channel. Also, in the embodiments of the presentinvention, a measurement cycle of the channel state of the forwardchannel (or the time interval between measurement periods) may bearbitrarily determined by the remote node as a function of the Dopplerfrequency of the forward channel, the maximum time allowed fortransmission, the elapsed time from the time of occurrence of the eventfor reverse channel transmission, and the QoS.

Further, in the embodiments of the present invention, a host node maytransmit the information of the measurement cycle of the forward channelto the remote node after determining the measurement cycle. For this, aparameter related to the random access channel (various parameters fordetermining the measurement cycle of the forward channel) may benotified via a broadcast channel transmitted in a forward direction.Also, the QoS level may be designated for each remote node based on aQoS at the time of service negotiation for each user.

FIG. 7 is a diagram illustrating an example of a message for the hostnode to transmit information about the measurement frequency of theforward channel state to the remote node, and the message includesvarious parameter items and their values. The message of FIG. 7 is underthe assumption that a parameter related to a random access channel istransmitted through a broadcast channel being transmitted via a forwardchannel, and is used when the host node transmits a threshold value of achannel for channel adaptive random access channel transmission.

The parameters illustrated in FIG. 7 are essential parameters for achannel adaptive random access channel, and assuming a channel conditionthat an average channel gain of a channel is normalized to 1, and arandom access channel is transmitted only when the normalized channelgain is greater than or equal to 0.1. In addition to this parameter, anequivalent effect may be produced by various methods including anaverage transmission probability (implying a probability that thechannel gain is greater than or equal to the particular thresholdvalue).

Besides this transmission condition of the random access channel, thehost node transmits various parameters for the measurement condition ofthe forward channel to the remote node. One of them is a minimum cyclein which the remote node is required to perform a forward channelmeasurement. In FIG. 7, it is designated that the remote node isrequired to measure the channel state of the forward channel at least 20times in 1 second. Also, FIG. 7 shows that a measurement frequency ofthe forward channel may differ based on the Doppler frequency of thechannel and QoS (may be used as a parameter representing a quality of aservice with a time delay).

As described in the foregoing, a method of notifying, by the host node,a minimum measurement frequency to the terminal was used in theembodiment of FIG. 7. However, in many cases, because the minimummeasurement frequency is determined by a Doppler frequency of a channel,a method in which a host node notifies a Doppler frequency of a channelor an estimated value of a minimum Doppler frequency, and a remote nodedetermines a measurement frequency or a minimum measurement frequencybased on the determined result, may be also used.

Meanwhile, the embodiments of the present invention additionally proposea method that improves the overall performance by changing thetransmission condition during transmission of a channel adaptive randomaccess channel. There may be many reasons of changing the transmissioncondition during transmission of the random access channel. In thisinstance, it is preferred to change the transmission condition toincrease the transmission probability of the access probe over timeafter initial transmission of the random access channel.

For example, assume that a total time T to transmit the random accesschannel is given. Because sufficient time is left at an initial stage inwhich transmission of the random access channel started, thetransmission condition may be set to have a low transmission probabilityby enabling standby until a good channel state appears. Lowering thetransmission probability implies that the forward channel (including theaccess probe) is transmitted only when the channel is in a relativelygood state, and also implies an increase of the threshold value in thechannel gain. Therefore, only when the channel gain of the forwardchannel (or the channel state estimated value of the reverse channel)exceeds the high threshold, the random access probe is transmitted.

However, even when the left time allowed to transmit the random accessprobe is small after time has passed, if a low transmission probabilityis maintained (implying that the channel threshold is maintained at ahigh level), there is a high possibility that transmission of the accessprobe within the total allowed time will fail. Accordingly, an optimumperformance can be achieved by resetting the channel threshold to alower value (implying changing the transmission probability of theaccess probe to a high level) when the allowed left time is insufficientafter time has passed. In sum, in the channel transmission of the remotenode, the embodiments of the present invention may variably reset thetransmission channel condition over time. Also, this transmissionchannel condition is preferably changed and set such that thetransmission probability of the reverse channel becomes relativelyhigher over time.

Similar to the method of setting the receiving cycle of the forwardchannel described previously, the threshold representing thetransmission condition may be also set adaptively based on at least oneof a Doppler frequency of the received forward channel, a time allowedto transmit the reverse channel, an elapsed time from the time ofoccurrence of an event that aims to transmit the reverse channel, or arequired level of a set QoS, and a request from the host. Thisoriginates from an essential attribute that both (the method of varyingthe measurement frequency of the forward channel and the method ofvarying the channel condition) should be managed differently based onthe channel state.

FIGS. 8a and 8b are diagrams illustrating methods of changing thetransmission condition in the channel transmission of the remote nodeaccording to another exemplary embodiment of the present invention, andshows a change in the threshold of the channel gain representing thechannel condition over time. Here, the channel gain may be a valueobtained by dividing an instantaneous channel gain of the forwardchannel by an average channel gain of the forward channel. Since it iswell known that a channel state of a reverse channel can be estimatedfrom a channel state of a forward channel in a time divisionduplex-based wireless communication system, it is obvious that this maybe represented by a channel gain or channel state of a reverse channel.Under this environment, the remote node transmits the access probe whenthe measurement value of the forward channel gain is greater than orequal to the set threshold, and otherwise, delays the transmission ofthe access probe.

In FIGS. 8a and 8b , determination is made on whether to transmit therandom access channel by setting the threshold value to be high at aninitial stage in which the remote node started transmission. However, itcan be seen that the threshold value of the channel gain changes to alow level over time. That is, operation may be implemented to increase atransmission probability of the access probe by reducing thetransmission threshold over time. The embodiment of FIG. 8a illustratesa case in which the threshold representing the transmission condition isobtained as a form of a continuous function based on time, in case thereceiver of the remote node always operates. The embodiment of FIG. 8billustrates an embodiment of a case in which the set threshold changessuddenly at a particular point in time. That is, the threshold valuechanges at several preset points in time. Actually, in case a state ofthe forward channel is measured at only certain several time periods,the threshold will be changed at only certain several points in time atwhich measurement is performed, as shown in the embodiment of FIG. 8 b.

Hereinabove, the embodiments of FIGS. 8a and 8b illustrated anembodiment of a case in which the transmission threshold is reduced tooptimize a left time allowed for transmission because the left timeallowed for transmission reduces over time. However, it is obvious thatduring transmission of the random access channel, the transmissioncondition or transmission threshold may be changed more strictly basedon a QoS change, a change in the Doppler frequency of the channel, or aninstruction by the host node.

FIG. 9 is a block diagram illustrating a remote node 900 communicatingwith a host node according to still another exemplary embodiment of thepresent invention, and the remote node 900 includes an antenna 10, areceiving unit 20, a transmitting unit 30, a channel estimating unit 40,and a control unit 50. Also, the remote node 900 may optionally includea Doppler frequency measuring unit 60 according to necessity. Eachcomponent of the remote node 900 of FIG. 9 corresponds to a series ofchannel transmission methods described previously through FIGS. 5 and 6,and thus, to avoid unnecessary overlapping, a brief description isprovided herein while focusing on the characteristics of the device.

The antenna 10 serves to receive a signal transmitted through a wirelesschannel and to send a signal that the remote node 900 intends totransmit.

The receiving unit 20 intermittently receives a forward channeltransmitted from a host node (not shown). In this instance, thereceiving unit 20 measures a forward channel by operating for only afirst period and does not measure a forward channel by failing tooperate for a second period apart from the first period. Accordingly, itis preferred to maintain minimum power consumption for the second periodduring which the receiving unit 20 does not operate. The first periodand the second period are arranged repetitively in the flow of time, anda time interval between the plurality of first periods (that is,representing a measurement cycle of the forward channel) may be variablyset.

In the viewpoint of implementation, the receiving unit 20 may include aradio frequency (RF) receiving block, a demodulation block, a channeldecoding block, and the like, to recover data from the signal receivedfrom the antenna 10. The RF receiving block may include a filter and anRF pre-processor, the demodulation block may include a fast Fouriertransform (FFT) operator to extract data carried on each subcarrier incase a wireless communication system uses an OFDM scheme, and thechannel decoding block may include a demodulator, a deinterleaver, and achannel decoder.

The channel estimating unit 40 estimates a state of a reverse channelfrom the remote node to the host node based on the forward channelreceived through the receiving unit 20. For example, the channelestimating unit 40 may estimate a receiving power of the received signalusing a pilot of a forward signal.

Meanwhile, the Doppler frequency measuring unit 60 may be optionallyincluded according to necessity. The Doppler frequency measuring unit 60estimates a Doppler frequency between the host node (not shown) and theremote node 900 using the signal received from the receiving unit 20.That is, the Doppler frequency measuring unit 60 provides the controlunit 50 with a basis for determination by estimating the Dopplerfrequency based on a change in the signal received through the forwardchannel.

The control unit 50 determines whether the state of the reverse channelestimated through the channel estimating unit 40 satisfies a presetchannel condition, and determines whether to transmit the reversechannel based on the determined result. For this, the control unit 50determines whether to transmit the reverse channel by comparing a stateestimate of the reverse channel calculated based on a channel gain ofthe received forward channel to a threshold representing the channelcondition. In this instance, it is preferred to reset the channelcondition variably over time. Meanwhile, the control unit 50 may set thethreshold in consideration of a QoS of a service required by a user, andmay set the threshold using the Doppler frequency measured by theDoppler frequency measuring unit 60.

Also, the control unit 50 controls the receiving unit 20 by determiningan operating cycle of the receiving unit 20 based on a determiningparameter. Here, the determining parameter may be at least one of aDoppler frequency of the received forward channel, a time allowed totransmit the reverse channel, an elapsed time from the time ofoccurrence of an event that aims to transmit the reverse channel, or arequired level of a set QoS, and a request from the host (not shown).Accordingly, the determining parameter may be received from the hostnode (not shown) or inputted by the user from the outside of the remotenode 900, or the control unit 50 alone may calculate the determiningparameter based on the forward channel received through the receivingunit 20 and at least one preset constraint condition.

The transmitting unit 30 transmits the reverse channel adaptively basedon the determination of the control unit 50. For this, the transmittingunit 30 generates a signal to be transmitted to a base station through arandom access channel by the control of the control unit 50. That is,the transmitting unit 30 converts a signal to be transmitted to a basestation via a random access channel into a form dedicated to transmitthrough a radio resource and provides it to the antenna 10, only whenthe control unit 50 allows the transmitting unit 30 to perform a randomaccess channel transmission.

In the viewpoint of implementation, the transmitting unit 30 may includea signal generating block, a channel coding block, a modulation block,and a RF transmitting block. The channel coding block may include amodulator, an interleaver, and a channel encoder, the modulation blockmay include an inverse fast Fourier transform (IFFT) operator to mapdata to each subcarrier in case a wireless communication system uses anOFDM scheme, and the RF transmitting block may include a filter and a RFpre-processor.

Meanwhile, the method of the present disclosure may be embodied ascomputer-readable code in computer-readable recording media. In thisinstance, the computer-readable recording media includes all types ofrecording devices for storing data that can be read by a computersystem. The computer-readable recording media includes, for example,read-only memory (ROM), random access memory (RAM), CD ROM disks,magnetic tape, floppy disks, optical media storage devices, and thelike, and may include implementation in a form of a carrier wave (forexample, transmission via an Internet). Also, the computer-readablerecording media can be distributed over network-coupled computer systemsso that the computer-readable code is stored and executed in adistributed fashion. Also, a functional program, code and code segmentsfor implementing the present disclosure can be easily inferred bycomputer programmers skilled in the technical field to which the presentdisclosure belongs.

Hereinabove, the present disclosure has been described with reference tovarious exemplary embodiments thereof. It will be understood by thoseskilled in the art that the present disclosure may be implemented inmodified form without departing from the essential features of thepresent disclosure. The exemplary embodiments should be considered indescriptive sense only and not for purposes of limitation. Therefore,the scope of the present disclosure is defined not by the detaileddescription of the invention but by the appended claims, and alldifferences within the equivalent scope thereto will be construed asbeing included in the present disclosure.

INDUSTRIAL APPLICABILITY

According to the embodiments of the present invention described in theforegoing, efficiency of channel transmission may be improved byenabling a remote node to transmit a reverse channel with a delay inconsideration of a channel state rather than making a responseimmediately upon receiving a forward channel from a host node, andunnecessary power required for channel reception may be reduced byintermittently measuring the forward channel being received from thehost node. Through this, when a battery is used in a mobilecommunication terminal or the like, an operating time of the terminalmay be greatly improved.

Also, according to the embodiments of the present invention described inthe foregoing, performance of reverse channel transmission may beoptimized by variably setting a channel condition in consideration of achange in the channel state. That is, a transmission power of the hostnode in the same performance may be reduced, while increasing adetection probability of the host node for the same transmission output.This allows channel adaptive random access channel transmission withhigher efficiency and lower power consumption.

The invention claimed is:
 1. A method for channel transmission of aremote node, the method comprising: intermittently receiving a forwardchannel transmitted from a host node, wherein the receiving of theforward channel comprises, measuring a state of the forward channel fora first period by enabling an operation of a receiver of the remote notefor the first period, and failing to measure the state of the forwardchannel for a second period by disabling the operation of the receiverfor the second period, wherein the first period and the second periodare arranged repetitively in a flow of time and a measurement cycle ofthe state of the forward channel is adjusted based on the receivedforward channel; estimating a state of a reverse channel from the remotenode to the host node based on the received forward channel; determiningwhether the estimated state of the reverse channel satisfies a presetchannel condition; and adaptively transmitting the reverse channel basedon the determined result.
 2. The method according to claim 1, whereinthe failing to measure the state of the forward channel for the secondperiod further comprises powering off a majority of blocks of the remotenode for the second period.
 3. The method according to claim 1, whereina time interval between the plurality of first periods arrangedrepetitively is variably set based on at least one of a Dopplerfrequency of the received forward channel, a time allowed to transmitthe reverse channel, an elapsed time from the time of occurrence of anevent that aims to transmit the reverse channel, a required level of aset quality of service (QoS), or a request from the host.
 4. The methodaccording to claim 3, wherein the measurement cycle of the state of theforward channel is set based on at least one of in inverse proportion tothe Doppler frequency of the received forward channel, in proportion tothe time allowed to transmit the reverse channel, in inverse proportionto the time of occurrence of the event that aims to transmit the reversechannel, in inverse proportion to the required level of the set qualityof service (QoS).
 5. The method according to claim 1, wherein thereceiving of the forward channel comprises: setting a next measurementtime; comparing the set next measurement time to a present time;measuring the state of the forward channel by enabling the operation ofthe receiver, when the next measurement time corresponds to the presenttime; and stopping, by the remote node, the operation of the receiverand standing by for a predetermined time, when the next measurement timedoes not correspond to the present time, wherein the comparing repeatsafter the standby for the predetermined time.
 6. The method according toclaim 1, wherein a transmission power for transmitting the reversechannel is determined by estimating the state of the reverse channelthrough measurement of a pilot channel included in the transmittedforward channel.
 7. The method according to claim 1, wherein the reversechannel is a random access channel (RACH), and the remote node is awireless communication terminal in conformity with a time divisionduplex (TDD) scheme.
 8. A method for channel transmission of a remotenode, the method comprising: receiving a forward channel transmittedfrom a host node, wherein the receiving of the forward channelcomprises, measuring a state of the forward channel for a first periodby enabling an operation of a receiver of the remote note for the firstperiod, and failing to measure the state of the forward channel for asecond period by disabling the operation of the receiver for the secondperiod, wherein the first period and the second period are arrangedrepetitively in a flow of time and a measurement cycle of the state ofthe forward channel is adjusted based on the received forward channel;estimating a state of a reverse channel from the remote node to the hostnode based on the received forward channel; determining whether theestimated state of the reverse channel satisfies a preset channelcondition; and adaptively transmitting the reverse channel based on thedetermined result, wherein the channel condition is variably reset overtime.
 9. The method according to claim 8, wherein the channel conditionis changed and set such that a transmission probability of the reversechannel becomes relatively higher over time.
 10. The method according toclaim 8, wherein a threshold representing the channel condition isvariably set based on at least one of a Doppler frequency of thereceived forward channel, a time allowed to transmit the reversechannel, an elapsed time from the time of occurrence of an event thataims to transmit the reverse channel, a required level of a set qualityof service (QoS), or a request from the host.
 11. A remote node,comprising: a receiving unit to intermittently receive a forward channeltransmitted from a host node, wherein the receiving unit measures astate of the forward channel by enabling an operation of the receivingunit for only a first period and does not measure the state of theforward channel by disabling the operation of the receiving unit for asecond period, wherein the first period and the second period arearranged repetitively in a flow of time and a measurement cycle of thestate of the forward channel is adjusted based on the received forwardchannel; a channel estimating unit to estimate a state of a reversechannel from the remote node to the host node based on the receivedforward channel; a control unit to determine whether the estimated stateof the reverse channel satisfies a preset channel condition anddetermine whether to transmit the reverse channel based on thedetermined result; and a transmitting unit to adaptively transmit thereverse channel based on the determination of the control unit.
 12. Theremote node according to claim 11, wherein a minimum measurementfrequency of the state of the forward channel is determined based on aDoppler frequency of the forward channel.
 13. The remote node accordingto claim 11, wherein a time interval between the plurality of firstperiods arranged repetitively is variably set based on at least one of aDoppler frequency of the received forward channel, a time allowed totransmit the reverse channel, an elapsed time from the time ofoccurrence of an event that aims to transmit the reverse channel, arequired level of a set quality of service (QoS), or a request from thehost.
 14. The remote node according to claim 12, wherein minimum powerconsumption is maintained for the second period during which thereceiving unit fails to operate.
 15. The remote node according to claim11, wherein the control unit controls the receiving unit by determiningan operating cycle of the receiving unit based on a determiningparameter, and the determining parameter is at least one of a Dopplerfrequency of the received forward channel, a time allowed to transmitthe reverse channel, an elapsed time from the time of occurrence of anevent that aims to transmit the reverse channel, a required level of aset quality of service (QoS), or a request from the host.
 16. The remotenode according to claim 15, wherein the determining parameter isreceived from the host or inputted by a user from an outside of theremote node.
 17. The remote node according to claim 15, wherein thedetermining parameter is calculated by the control unit based on thereceived forward channel and at least one preset constraint condition.18. The remote node according to claim 11, wherein the channel conditionis variably reset over time.
 19. The remote node according to claim 11,wherein the control unit determines whether to transmit the reversechannel by comparing a state estimate of the reverse channel calculatedbased on a channel gain of the received forward channel to a thresholdrepresenting the channel condition.
 20. The remote node according toclaim 11, wherein a threshold representing the channel condition isvariably set based on at least one of a Doppler frequency of thereceived forward channel, a time allowed to transmit the reversechannel, an elapsed time from the time of occurrence of an event thataims to transmit the reverse channel, a required level of a set qualityof service (QoS), or a request from the host.